The object of the present invention is to increase the efficiency of operations to remove undesirable materials which normally accumulate at the bottom of storage tanks. It involves the use of a bottom whose center is at a level than lower that of the edges, and aims to concentrate at the center of the bottom the residues which are to be drained.
It also involves the use of a drainage channel in the form of a ramp, which runs from the center of the tank bottom to the edges. This ramp is inclined sufficiently to allow the drainage of the undesirable materials out of the tank.